The invention is generally related to dampeners for reciprocating air-cooled engines and the method of applying the dampener to the engine. The invention is specifically related to resilient cooling fin dampeners for aircraft engines and modifications of the intake manifold and propeller servo control system for the purpose of reducing the forced vibrational frequency of the engine to prevent damage to the engine by self-induced vibrations.
In general, aircraft engines are prone to have vibration problems, as they must be light in weight and have a relatively high horsepower, as well as being air-cooled. The problems of vibration are particularly acute in reciprocating type air-cooled aircraft engines, due to the reciprocating firing motion of the engine. In the prior art, little has been done to prevent or overcome excessive vibration problems in reciprocating air-cooled aircraft engines, except by way of strengthening the damage-prone parts of the engine and spreading the operational frequency of the engine by operating engine-driven pumps, and other accessories, at speeds which are fractionally proportionally different from the crankshaft speed or firing or the frequency of the engine. In strengthening of the engine structure to prevent damage fin dampeners have been constructed to be mounted between and on the end portion of the cooling fins, primarily to prevent the fin from being broken off. The prior art fin dampener and strengthening structures have a single strip of resilient material, specifically rubber, which is pressed into the outer portion of the cooling fins and is attached to the fins by the heat of the engine which cures or sets the material. Other known fin dampener structures include a comb-like structure, having the teeth extending between the fins with a clasp encircling the teeth and rightenable to compress them circumferentially thus expanding it between the fins to hold it in place. A prior art fin dampener structure is known which extends from the outer portion of the fins completely to the attachment point of the fins with such being retained in place by an adhesive material. No prior art device or devices are known which are specifically constructed for use with an air-cooled multi-cylinder aircraft type engine to control the vibrational characteristics or natural operating frequency of the engine in an attempt to prevent the operating frequency from becoming resonant or causing substantial structural damage to the engine.
Reciprocating type internal combustion aircraft engines are inherently a vibration generating body in an aircraft due to the inherent reciprocating or oscillating motion. Reciprocating type aircraft engines are balanced internally so they will perform their operation with a minimum of unbalance: however, in practice the engines do vibrate considerably and produce a quantity of often objectionable noise. Engine vibration and noise affect engine fatigue, airframe fatigue and pilot fatigue. A great many engine failures and pilot failures or malfunctions can be attributed to engine vibration and noise associated with the operating the reciprocating type of engine. The specific engine failures or malfunctions which can be substantially attributed to vibrationally induced factors include, cooling fin fractures, engine cylinder fractures, piston ring fractures, and crankshaft and connecting rod fractures. It is well known in the art that fatigue, due to noise and vibration, will crack and propagate cracks in materials subjected to such forces, and it is these forces which cause fracture or other failure in the identified parts of an engine or other parts of an engine connected with these components.
The problem of engine failure and malfunction has long been a critical problem in aviation and it has been studied in depth. One such study was conducted by the United States National Transportation Safety Board and documented in the report entitled, "Special Study Accidents Involving Engine Failure/Malfunction, U.S. General Aviation, 1965-1969." This report is published by the National Transportation Safety Board as report number NTSB-AAS-72-10, it was adopted Nov. 29, 1972. This special study presents a record of engine failure/malfunction accidents for fixed-wing aircraft, all of which occurred in all operations of U.S. general aviation, during the period of 1965-1969. It includes a complete comparison of engine-failure accident rates for single-engine and multi-engine aircraft. Analysis are included concerning causes and related factors of engine-failure accidents by selected makes and models of aircraft and engines. It includes tables, comparing cause/factors for the accidents and severity of the accidents for all fixed-wing aircraft along with single-engine and multi-engine fixed-wing aircraft.
The invention disclosed herein is a result of studies of and experiments made with a Continental IO-470 and IO-520 series engines. The IO-470 and IO-520 series of engines are manufactured in several models for different applications however they are basically structurally the same. These engines are essentially structurally identical with the IO-520 series having a larger displacement and horsepower rating. The following are exerpts from the identified report, from the portion related to analysis of engine failure/malfunction for these particular engines. A close examination of the special study report indicates that these identified engines had a significantly higher-than-expected involvement in individual power plant cause/factor citations. It is to be noted that the power plant of an aircraft was cited as a probable cause/related factor in over 44 percent of the engine-failure accidents. The predominant power plant cause/factor citation include in part; master and connecting rods, cylinder assembly, piston and piston rings, and crankshaft. In regard to the IO-470 model engine, the cause/factor citations were specific to the engine cylinder assemblies, master and connecting rods, crankshaft, fuel system lines and fittings. In regard to the Continental IO-520 engine, the cause/factor citations were specific to the piston, piston rings and crankshaft. The specific engine elements cited are the elements of the engine which would obviously be the most likely to have vibration and fatigue damage because they are so closely related to the rotating and reciprocating motion of the engine. In use, the two identified engines are normally used in the following aircraft: Beechcraft Model 35; Cessna 180; Cessna 182, Cessna 206, Cessna 188, and Navion Model L-17. In the special study report, detailed cause/factors for particular aircraft make and model are compared with those of other aircraft. In this comparison a normal approximation the nomial technique was used, wherein the accounts of a cause/factor for a particular assembly, engine, aircraft, etc., is comparable to same appearance for all aircraft involved in the study. The special study report reveals that most of the engine-failure accidents for each aircraft make and model were caused by a pilot-in-command error, such as inadequate preflight preparation and/or planning, mismanagement of fuel, and improper operation of power plant controls. Explaining why a particular aircraft has a higher than expected percentage of engine failure accidents for a specific power plant cause/factor involves an inspection of the engines installed in those particular aircrart. In regard to the identified engine, the frequency of piston and piston ring problems are significantly higher than expected for the Navion L-17 and the Cessna 210 than in the Beechcraft. The Navion L-17 uses the Continental IO-470 model engine and the Cessna 210 is equipped with the Continental IO-470 and the Continental IO-520 engine. The IO-470 engine in the Beechcraft Model 35 aircraft experienced a higher than expected involvement in the fuel system pumps area. In regard to the Cessna 210 aircraft, the following engine elements and percentages are the parts of the engine structure which were cited as a cause/factor in the respective percent of total accidents: piston, piston rings-6.9%, cylinder assembly-5.2%, crankshaft-3.4 %, and master and connecting rods-3.4%. The expected percentage of engine structure failure or malfunction for the noted elements is 2%, 2%, 1.8%, and 2.5%, respectively. It is to be noted that the actual percentages are significantly higher than the actual percentages in this instance substantially higher than the expected percentages.
In the special study, a total of 3,312 engine-failure accidents were condiered. The accidents studied do not include home-built or experimental category of aircraft. The pilot was the cause/factor in the majority (64.31%) of the accidents and the power plant was a cause/factor in 38.82% of the accidents. Summerizing these comparisons of power plant cause/factors, some of them appeared to be significantly higher than expected in percentage of involvement to be vibration induced or caused. These two identified engines, according to reports, appear to be more seriously affected by vibrations of normal engine operation than do the other engines of the group studied. No prior art device is known which is operative to reduce the vibrational characteristics of a reciprocating type aircraft engine, particularly the identified engines so the vibrational response of the engine is effectively lowered to prevent damage and failures of the type outlined in the report on the special study.